Indexed on: 01 Feb '88Published on: 01 Feb '88Published in: Physics and Chemistry of Minerals
Shock recovery experiments for single crystal and powdered specimens of TiO2 with the rutile structure were performed in the pressure range up to 72 GPa. Single crystal specimens were shocked parallel to ,  and  directions. X-ray powder diffraction analysis showed that the amount of α-PbO2 type TiO2 produced by shock-loading depended strongly on the shock propagation direction. The maximum yield (about 70%) was observed for shock loading to 36 GPa parallel to the  direction. In the  shock direction, the yield is much smaller than that of the  direction. This anisotropic yield was consistent with the observed anisotropy of the phase transition pressure in shock compression measurements. However, transformation to the α-PbO2 type cannot explain the large volume change observed above about 20 GPa. On the basis of the high pressure behavior of MnF2, we assumed that the high pressure phase was either fluorite or distorted fluorite type and that the phase conversion to the α-PbO2 type was induced spontaneously in the pressure reduction process.We present a displacive mechanism of phase transition under shock compression from the rutile structure to the fluorite structure, in which the rutile  is shown to correspond to the fluorite  or  and the rutile  to the fluorite . Direct evidence is obtained by examining the  shocked specimen by high resolution electron microscopy.